Allograft reconstruction for humeral head defects in the setting of shoulder instability: a systematic review

Background Glenohumeral joint instability and dislocation are common orthopedic pathologies that can produce osseous humeral head defects such as Hill-Sachs (HS) or Reverse Hill-Sachs (RHS) lesions. Numerous reconstruction techniques have been reported in the literature, including remplissage, disimpaction, and allograft reconstruction. No group has previously assessed the outcomes of allograft reconstruction for RHS lesions, nor compared the outcomes of allograft reconstruction for HS and RHS lesions. In this study, we aim to provide a comprehensive assessment of osteochondral allograft reconstruction for the distinct pathologies of RHS lesions and HS lesions by comparing postreconstruction patient-reported outcomes, complications, and radiographic assessments for each lesion. Methods Using Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, a systematic review was performed to identify and include studies that reported patient outcomes after the use of osteochondral allografts in the reconstruction of HS or RHS lesions of the humeral head. A comprehensive search of the Google Scholar, PubMed, and Embase databases was conducted with the key terms “allograft,” “Hill-Sachs,” and “reverse Hill-Sachs.” Results Eight studies, with a total of 84 patients, were included for review. Of the 84 allograft-treated patients, there were 44 patients with HS lesions and 40 patients with RHS lesions. The average patient age was 27.3 years for HS lesions and 43.0 years for RHS lesions. Postoperative range of motion and average Constant-Murley score (87.9 for HS and 80.1 for RHS) appeared to be greater for those with HS lesions. In addition, 20.5% of HS patients experienced postoperative complications, whereas 42.5% of RHS patients had postoperative complications (P = .03). HS and RHS patients experienced similar proportions of graft resorption or collapse rate (22.7% for HS and 12.5% for RHS; P = .2). Conclusion Patient-reported outcomes indicate that osteochondral allograft reconstruction for large RHS and HS lesions is an acceptable intervention. RHS patients had lower rates of graft resorption and collapse but worse postoperative range of motion and functional outcomes, although these differences were not statistically significant. HS patients experienced significantly fewer complications than those with RHS lesions.

humeral head, and are reported in up to 86% of posterior shoulder dislocations. 13 There are numerous surgical techniques to address the humeral head following HS or RHS lesions, including autograft or allograft augmentation, remplissage, disimpaction, and prosthesis replacement. Of the methods used for HS and RHS lesions, allograft reconstruction is often used for the management of large defects with or without glenoid bone injury. 11 No systematic review exists in the current literature assessing outcomes of allograft reconstruction in RHS lesions. Our study is the first to do so through patient-reported outcomes, complications, and radiographic assessment. In addition, this is the first systematic review to compare the results of allograft reconstruction between HS and RHS lesions. We hypothesized that osteochondral allograft reconstruction will provide similar and satisfactory postoperative outcomes for both HS and RHS lesions.

Methods
Using Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, a systematic review was performed to identify studies that reported patient outcomes after the use of osteochondral allografts in the reconstruction of HS or RHS lesions of the humeral head. A comprehensive search of the Google Scholar, PubMed, and Embase databases was conducted by using different combinations of the key terms "allograft," "Hill-Sachs," and "reverse Hill-Sachs," including (allograft AND Hill-Sachs), (allograft AND reverse Hill-Sachs), (allograft AND Hill-Sachs AND reverse Hill-Sachs), and (allograft AND (Hill-Sachs OR reverse Hill-Sachs)). Our inclusion criteria consisted of level I-IV studies, articles that reported on allograft reconstruction of humeral head defects, and studies that reported clinical and/or radiographic outcomes. Articles were excluded if allograft bone impaction occurred without restoration. Study populations of less than 3 patients, review articles, cadaveric studies, biomechanical studies, and studies not available in English were also excluded.
All duplicate studies were initially removed, and abstracts were reviewed in detail by 2 authors (A.A.Y. and A.G.D.). Disagreements between these authors were arbitrated by the senior author (E.W.B.). Following the initial screening, articles were assessed via full-text review; any disagreements were once again arbitrated by the senior author. The final articles included for review reported patient outcomes after osteochondral allograft reconstruction of HS or RHS lesions of the humeral head.

Study selection
Initial database searches yielded 1657 records. After duplicates were removed, 913 studies were screened and assessed for eligibility. A total of 8 studies containing 84 patients met inclusion and exclusion criteria in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines (Fig. 1).

Study characteristics
All 8 studies were case series. Three studies 3,8,9,15 evaluated 41 patients with HS lesions. Four 2,4,5,7,10 studies assessed 38 patients with RHS lesions. One study evaluated 2 RHS patients and 3 patients with humeral head defects due to anterior instability, interpreted by our authors as HS lesions. 12 In total, our study population was composed of 84 patients, with 44 HS lesions and 40 RHS lesions. The average patient age was 27.3 years for HS lesions and 43.0 years for RHS lesions. The mean follow-up period was 39.5 months for HS lesions and 93.6 months for RHS lesions (Table I).

Allograft types used
A variety of osteochondral allografts were used for both HS and RHS patients. For HS lesions, fresh frozen femoral head, irradiated humeral head, osteochondral allograft plugs, and fresh mushroom cap osteochondral allografts were used. 3,8,9,12,15 Of these, the most used methods were fresh frozen femoral head (21, 47.7%), irradiated

Range of motion
Range of motion was assessed in 3 of the 4 HS studies (41 total patients). Zhuo et al demonstrated that postoperatively, patients recovered near full range of motion in forward elevation (170 ± 8.2 ), external rotation (61.8 ± 8.9 ), and internal rotation (T8). 15 Miniaci et al demonstrated that the average loss of external rotation improved by 30 (from 40 loss preoperatively to just 10 loss postoperatively; Table II). 8,9 Two of the 5 RHS studies (19 total patients) evaluated postoperative range of motion. Martinez

Functional outcomes
Several functional outcome surveys were evaluated in the collected studies, including the American Shoulder and Elbow (ASES) score; Constant-Murley score; Rowe score; University of California, Los Angeles score; Western Ontario Shoulder Instability Index score; Visual Analog Scale (VAS) pain score; Subjective Shoulder Value; Simple Shoulder Test score; and the 12-Item Short Form Survey's Physical Component. Only the ASES, Constant-Murley, and VAS pain scores were reported in more than one HS study (Table II). Meanwhile, only the Constant-Murley score was reported in more than one RHS study (Table III).
Postoperative Constant-Murley score was assessed in 2 of the 4 HS studies (37 total patients), with an average score of 87.9. 8,9,15 Four of the 5 RHS studies (38 total patients) reported Constant-Murley scores, with an average score of 80.1. 2,4,5,7,10 Postoperative ASES score was reported in 3 of the 4 HS studies (26 total patients), with an average score of 93.1. 3,12,15 Only one RHS study (2 total patients) reported ASES score, with an average score of 79. 12 VAS pain score was reported in 2 of the 4 HS studies (21 total patients), with improvements in average shoulder pain score after operation in both studies. 8,9,12 Only one RHS study (2 patients) reported average improvement in VAS shoulder pain score after operation. 12

Patient satisfaction
Patient satisfaction was reported in 3 HS studies (40 total patients), with an average satisfaction rate of 95% (Table II). 8,9,12,15 Patient satisfaction rate was only provided in one RHS study (2 total patients) and resulted in an average rate of 100% (Table III). 12

Discussion
To our knowledge, this is the first study to provide a comprehensive assessment of allograft reconstruction for RHS lesions through patient-reported outcomes, complications, and radiographic assessment. By extension, this study is also the first to compare the results of allograft reconstruction between HS and RHS lesions. Following our review, we found that osteochondral allograft reconstruction for HS and RHS lesions provides similar and satisfactory outcomes. When comparing the 2 patient populations, HS patients appeared to have greater average functional scores and postoperative range of motion. In addition, postoperative complication rates for HS patients were found to be significantly lower compared with RHS patients. Although it appears that relatively fewer RHS patients reported graft resorption or collapse, there was no statistically significant difference found between the 2 groups.
For both functional scores and postoperative range of motion, HS patients appeared to experience better outcomes than their RHS counterparts (Tables II and III). However, after further examination, we believe these values are potentially skewed by the differences in average patient age (27.3 years for HS and 43.0 for RHS) and mean follow-up period (39.5 months for HS and 93.6 months for RHS) seen in Table I. A strong argument supporting this claim can be seen in Martinez et al and Gerber et al, where the mean follow-up periods (122 and 143.3 months respectively) were the longest among all HS and RHS studies. Compared with the rest of the studies, these 2 RHS studies reported the lowest functional scores and postoperative range of motion values, while also reporting the highest rates of complications, another potential explanation for the worse outcomes. 4,5,7 As for the significant difference in postoperative complication rates, 20.5% of HS patients, and 42.5% of RHS patients reported complications. [2][3][4][5][7][8][9][10]12,15 Once again, we believe this stark difference is potentially due to the older average age and longer mean follow-up period for RHS patients. With an older population and a longer follow-up interval, RHS patients had more time to potentially develop postoperative complications, especially those that develop via arthritic processes. This is corroborated by the fact that most RHS complications were reported by Martinez et al and Gerber et al, despite these studies comprising less than half of the RHS study patient population. 2,4,5,7,10,12 Although HS patients fared significantly better in terms of complications, there was no statistically significant difference found between HS and RHS patients in terms of graft resorption or collapse rate. [2][3][4][5][7][8][9][10]12,15 Nonetheless, clinical significance of these findings should not be undervalued, as nearly one-fourth of HS patients and one-eighth of RHS patients experienced graft resorption or collapse. In addition, Zhuo et al reported significant differences between their resorption and nonresorption groups in terms of age, duration of instability, and preoperative size of HS lesion. 15 Taking these findings into account, it is critical to preoperatively evaluate HS patients on an individual basis to ensure chances of graft resorption or collapse remain low. As for RHS patients, more research is needed to be done to determine if differences are found between resorption and nonresorption groups.
As with every surgical intervention, allograft reconstruction for an HS or RHS lesion has its advantages and disadvantages. To date, prior literature supports the use of allografts as a powerful tool for reconstruction of the humeral head. Benefits such as high functional outcome scores and improvements in range of motion must be weighed against the risks of postoperative complications and graft resorption or collapse. Our findings can be of great value, as they provide clinicians an up-to-date summary of allograft reconstruction for both disease processes. However, further work is needed to assess the optimal allograft type for humeral head reconstruction.

Limitations
Our study has several limitations. With limited published literature on allograft reconstruction for RHS lesions, the primary limitation of our study is small patient populations. Demographic differences between RHS and HS groups, as well as differences in the underlying pathology, limit our study conclusions. In addition, variation in the individual studies, including surgical techniques, follow-up periods, and allograft types, should not be overlooked. It is also difficult to directly compare the outcomes of the studies, as few patient-reported outcomes or range of motion measures were consistent between studies. Finally, as most studies lacked preoperative assessment values, we could not generate effect sizes for meta-analysis.

Conclusion
In this study, we demonstrated that humeral head defects reconstructed with osteochondral allograft produce similar and satisfactory outcomes for large HS and RHS lesions. RHS patients had lower rates of graft resorption and collapse but worse postoperative range of motion and functional outcomes, although these differences were not statistically significant. HS patients experienced significantly fewer complications than those with RHS lesions. Given the limited overlap in reported outcomes between studies and the paucity of published cases of HS and RHS allograft reconstruction, more studies are needed to better characterize patient populations and predict patient outcomes.

Disclaimers
Funding: No funding was disclosed by the authors. Conflicts of interest: The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.